chore: bump to 0.8.2, changelog for the PTY exit-signal fidelity fix

- version 0.8.1 -> 0.8.2 (patch: behavior-only bug fix in the local
  feature's PTY waiter from db0b1fc; ADR-004 decision 1's negative-code
  convention now holds on the PTY path; no API, wire-format, or
  dependency change)
- CHANGELOG entry for 0.8.2 (review #004 resolution: the waitpid reap
  mechanism, the signal round-trip notes, the tests, the docs)
- finish the em-dash sweep in prose 58da42a missed: doc comments in
  tests/ (negotiation, pipe, pty, common) and fuzz/shared
  (control_json, negotiation_frame, session_opseq); prose rewrites
  only, no code, JSON literals, or wire shapes touched
- README checked: no version pins, nothing to update

Verification: cargo test; cargo test --all-features; cargo clippy
--all-targets -D warnings (default and --all-features); cargo fmt
--check; cargo doc --no-deps; fuzz/shared corpus replay (9 seeds pass);
cargo check + clippy for wasm32-unknown-unknown -D warnings; cargo
publish --dry-run --allow-dirty (43 files, 194.4 KiB); detached
campaigns over the four targets (chunk_frame 632s, negotiation_frame
602s, control_json 610s, session_opseq 608s) all exiting 0 with
0 crash/oom/timeout findings.

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "alktty"
-version = "0.8.1"
+version = "0.8.2"
 edition = "2021"
 rust-version = "1.88"
 license = "MIT OR Apache-2.0"